Category Archive: Metrics

Jun
03

Robustness-Based Tuning

Robustness Map

Before tuning calculations are applied in a control loop, it is good to consider how much the process gain and deadtime can change before the loop becomes unstable. In the DeltaV control system, this information is provided using a robustness plot that shows gain margin and phase margin as illustrated below. Information on this type …

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Mar
25

Split Range Setup

Split Range Control

One of the most common ways of addressing multiple process inputs is split range control. A splitter block, which appears as one valve to the PID block, can be used in the control strategy to define a fixed relationship between the controller output and each manipulated process input. In Advanced Control Foundation – Tools, Techniques, …

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Mar
18

Impact of Changing Process Gain

non-linear valve characteristics

From a control perspective, it is highly desirable that the process gain is constant. If the process gain is constant, then the same proportional gain can be used over the entire operating range of the control loop. Using a control valve as an example, if the valve characteristic was not properly selected based on the …

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Mar
11

Evaluating Valve/Actuator Performance

Impact of Sticky Valve on Control

When a control loop is placed in automatic control, it is easy to detect if a valve or actuator is not responding correctly to the control system. As discussed in Chapter 3 of Advanced Control Foundation – Tools, Techniques and Application, this can be done by observing the response of the controlled parameter to control …

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Mar
04

Addressing Incorrect Tuning

DCS tuning Support

A Loop tuning has a significant impact on control loop utilization and performance. Controller tuning parameters can be easily changed over a wide range to adjust loop operation for various process requirements. However, some expertise in tuning is required even when advanced control tools are used, and there is a chance that the behavior of …

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Feb
25

Identifying Transmitter Problems

Standard PID Parameters

One of the most obvious reasons for poor control utilization is a broken or unreliable transmitter or sensor. As addressed in Chapter 3 of Advanced Control Foundation – Tools, Techniques, and Applications, if the control system is designed to be consistent with the international function block standard, IEC 61804, the status attribute is always communicated …

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Feb
18

Improving Control Utilization

Addressing Problems That Impact Control Utilization

When the utilization of a control loop is found to be low during normal plant operation, the measurement or control problems that prevent the control loop from functioning in its normal (designed) mode of operation should be further explored. In Chapter 3 of Advanced Control Foundation – Tools, Techniques, and Applications we outline the steps …

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Feb
11

Control Utilization

Pulp and Paper Mill Control Utilization

It can be shocking to examine control utilization in a plant where performance tools have not been installed and/or not used. For example, in the mid-1980s a control survey was conducted at a major pulp and paper plant where the control system had recently been updated to the latest distributed control system. At that time …

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Feb
04

Evaluating Control Performance

A plant operator is usually responsible for managing one or more process areas, with (potentially) hundreds of control loops and process measurements in each area. The operator’s job is made easier if the control loops in these process areas are in automatic mode and can compensate automatically for disturbances and maintain the operating conditions the …

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Jan
28

Assessment of Control Performance

Assessment of Control Performance

To achieve the maximum benefit, the performance monitoring tools that are installed in control systems to evaluate plant control performance should contain features to support both analysis and diagnostics. Process Analysis is the examination of a process, its elements, and their relationships. Process Diagnostics is the investigation of the cause or nature of a process …

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